Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0637—Accessories therefor
  • B22D11/064—Accessories therefor for supplying molten metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
  • B22D11/18—Controlling or regulating processes or operations for pouring
  • B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level

Definitions

• the invention relates to the continuous casting of metal strip, in particular of aluminum or aluminum alloy strip.
• a machine (1) for continuous casting of metal strip (3) generally contains at least two identical cylinders (1 A and IB) located face to face and a device for injection (6) comprising a tundish (24) and an injector (23).
• the cylinders are separated by a space (or air gap) E substantially equal to the thickness of the metal strip to be produced and rotating in opposite directions to one another.
• the metal (2) is supplied, in the liquid state, to one side of the space, using the injection device (6), solidifies on contact with the cylinders and leaves in the solid state, on the other side of the air gap, in the form of a strip (3) having a nominal thickness Eo.
• the metal solidifies between the two cylinders, at what is known as the solidification front (5). With such a device, bands ranging from a few centimeters thick to a few millimeters or less can be produced.
• the regularity of the thickness of the strip obtained in particular for small thicknesses, because this regularity determines the properties of use of the strip, in particular of its ability to be transformed.
• Several factors are known to be responsible for the thickness fluctuations, which fluctuations consist essentially of variations and irregularities.
• fluctuations in the level of the liquid metal contained in the injection device generate fluctuations in the thickness of the strip.
• the height of the sheet of metal contained in the injection device is of the order of 40 to 50 mm.
• the injection device (6) is supplied using a chute (7) provided with means (16, 17) for regulating the flow of liquid metal poured into the casting tray (24).
• the feed chute (7) is supplied with liquid metal (8) by a holding furnace (which is not illustrated).
• a float / shutter (16) covers an opening (17) arranged at the end of the feed chute (7) and cooperates with it so as to allow a flow of liquid metal whose flow is function of the float / obturator (16).
• the latter floats on the surface of the liquid metal (2), follows the variations in the height H of this metal and limits the flow of metal (18) as a function of the height of the metal level.
• the level of liquid metal is then regulated purely mechanically. With such a device, for a typical flow rate of 3 tonnes / hour, the height fluctuations of the metal level are at best of the order of ⁇ 1 mm.
• the injection device (6) is supplied using a feed chute (7) provided with means (9-15) for regulating the flow of liquid metal poured into the injection device according to a measured height.
• the regulation means (9-15) comprise a metal level sensor (11), which is typically a capacitive sensor, an electronic regulation circuit (10) comprising a detection circuit (12) and a control circuit (13 ), an adjustable opening (9) arranged in the bottom of the feed chute (7).
• the opening (9) can be closed in a controlled manner by a shutter means (15) moved vertically by an actuator (14) under the control of the circuit (13).
• the Applicant has therefore sought solutions which make it possible to limit the fluctuations, that is to say the variations and irregularities, in the thickness of the metal strips obtained by continuous casting to values less than ⁇ 0.05 mm, while allowing large flows of liquid metal, namely flows of the order of 3 tonnes / h or more, and the production of strips of large width, namely of a width typically greater than 1 meter, or even greater than 2 meters.
• the Applicant has found that the fluctuations in thickness of the strip coming from a continuous casting machine remain substantially the same, in absolute value, whatever the thickness of the strip. Under these conditions, a range of fluctuations which is tolerable for thick bands becomes unacceptable for bands of thin thickness.
• the devices of the prior art make it possible to limit the amplitude of the thickness fluctuations at best to about ⁇ 0.05 mm whatever the thickness of the strip. For example, with the known devices, it is not possible to cast strips of a thickness less than 5 mm with a precision on the thickness better than ⁇ 1%.
• the fluctuations are generally greater the greater the width of the strip.
• the Applicant has had the idea of using Archimedes' thrust to vary the level of liquid metal contained in the injection device in a simple and controllable manner.
• the displacement of a plunger in the liquid metal thus makes it possible to finely control the height of the liquid metal, and therefore the hydrostatic pressure which results therefrom, without intervening on the supply of liquid metal.
• Liquid metal level and flow control can therefore be practically decoupled.
• the invention has the advantage of separating the fine control of the level of liquid metal and the regulation of the supply of liquid metal.
• liquid metal feed which mainly aims at controlling the flow rate of liquid metal feed.
• the subject of the invention is a method for controlling the height H of liquid metal of an injection device of a machine for continuously casting metal strips, method in which: - a determined part P of at least is immersed a plunger in said liquid metal;
• the, or at least one, plunger is moved in the liquid metal so as to modify the volume of the immersed part of the plunger, to cause a displacement of the level of the liquid metal under the effect of hydrostatic pressure and to modify the said height H.
• the displacement of a plunger may consist in lowering it a little when the level of the liquid metal is too low and, conversely, raising it a little when the level is too high.
• the required displacement can be determined by a simple algorithm which is based on the difference between a measured height H of liquid metal and a reference value Ho and which takes account of the geometry of the plunger (s) and of the device d 'injection.
• the algorithm is typically an inverse function of the difference between the measured height H and the set height Ho (and more advantageously a function of the difference between the measured height Hc and a set height Hco).
• the algorithm can be more elaborate and can be, for example, a PID (proportional-integral-differential) algorithm.
• the invention also has the advantage of allowing precise control, that is to say an adjustment and / or regulation of the height of the liquid metal without significant modification of the hydrostatic pressure.
• the nature of the material of which the plunger (s) is made plays little role in the precision of the process, this which is not the case for processes or devices based on the flotation of one of the control means.
• the invention also relates to a device for controlling the height H of the liquid metal contained in an injection device of a continuous casting machine, capable of implementing the method of the invention.
• the subject of the invention is also a process for the continuous casting of a metal strip, characterized in that the height H of the liquid metal contained in an injection device is controlled using the control process of the invention.
• the invention also relates to a continuous casting machine for a metal strip, characterized in that it includes a device for controlling the height H of the liquid metal according to the invention.
• the invention is particularly advantageous when the metal strips (3) have a width greater than or equal to approximately 1000 mm, or even greater than or equal to approximately 2000 mm.
• FIG. 1 shows schematically the basic elements of a continuous casting machine.
• FIG. 2 represents two devices of the prior art which make it possible to control the flow of metal and the height H of the level of liquid metal in an injection device.
• FIG. 3 illustrates the operating principle of the method for controlling the level of liquid metal according to the invention.
• FIG. 4 schematically illustrates a first device of the invention.
• FIG. 5 schematically illustrates a second device according to the invention.
• FIG. 6 represents an embodiment of the device according to the invention.
• the method for controlling the height H of liquid metal (2) of an injection device (6) of a continuous casting machine (1) of metal strips (3) according to the invention is characterized in that:
• the (at least one or each) plunger (30) is moved in the liquid metal (2) so as to modify the volume of the submerged part P of the plunger, to cause a displacement of the level (20) of the liquid metal (2 ) under the effect of hydrostatic pressure and to modify said height H.
• the injection device (6) comprises a feed opening (19) and an outlet opening (21) having a width substantially equal to that of the strip (3) to be produced.
• the injector (6) is supplied with liquid metal using a chute (7), which pours liquid metal (8) into the casting tank (24) through the feed opening (19).
• the metal strip (3) leaves the air gap E in a direction (22) substantially horizontal or slightly inclined relative to the horizontal.
• the plunger (30) is immersed in the liquid metal (2) contained in the casting tank (24), which is integral with the injector (23), so that the control of the level of liquid metal takes place directly in the injection device (6) (and not in the feed chute or more upstream, which makes it possible to decouple the flow control and the metal level control).
• the invention is particularly suitable for cases where the height Hc of metal between the center of the injector and the free surface of the molten metal in the tundish is small compared to the width of the strip (Hc is typically between 5 and 50 mm while the width is typically greater than about 1000 mm).
• the (at least one or each) plunger is moved as a function of a measured value of the level (20) of the liquid metal. More specifically, the method of the invention is characterized in that:
• the measured height H is compared to the set value Ho in order to determine the displacement of the plunger (s).
• the measured height H is compared to the set value Ho and the plunger is moved in inverse function to the difference between the measured height H and the set height Ho.
• the displacement of the plunger (s) (30) may include additional immersion and emersion operations. For example :
• - a determined complementary part ⁇ P + of the (at least one or each) plunger (30) is immersed when H ⁇ Ho, so as to raise the level (20) of the liquid metal (2) and to increase said height H ;
• - a determined part ⁇ P- is made to emerge from (at least one or each) plunger (30) when H> Ho, so as to lower the level (20) of the liquid metal (2) and to reduce said height H.
• the partial immersion or emersion of the plunger makes it possible to vary the height so as to correct the differences between the measured value H and the reference value Ho.
• Said determined quantities ⁇ P + and ⁇ P-, for the lowering or raising of, or each, plunger (30) typically depend on the difference between H and Ho, the shape of the plunger (s) (30) and the shape of the device injection (6).
• These quantities can be determined by geometric calculation, for example using a simple algorithm based on the difference between H and Ho (and therefore based on the volumes of metal to be moved) and taking into account the geometry of (the ) plunger (s) and injection device.
• ⁇ P + and ⁇ P- can be given by the volume Vm of metal respectively below and above the setpoint level, corresponding to the difference between the actual volume of liquid metal and the volume delimited by the setpoint level, the internal surface of the tundish and the solidification front.
• the volume Vm is approximately equal to the product of the area of the free surface (20) of the liquid metal (2) and the difference between the set height Ho and the measured height H.
• the plunger (s) (30) may (may) have any shape, such as a cylindrical or conical shape.
• the shape and surface area of the plunger (s) are adjusted to ensure the required precision (when a plunger is submerged to its reference depth).
• At least one plunger is of cylindrical shape of circular section S and the main axis of which is perpendicular to the free surface (20) of the liquid metal (2), in which case the (or each) plunger can be moved vertically d 'a distance ⁇ X approximately equal to (H - Ho) x So / S, where So is the area of the free surface (20) of the liquid metal (2) contained in the injection device (6). If H is less than Ho, then ⁇ H is negative and the plunger can be lowered; if H is greater than Ho, then ⁇ H is positive and the plunger can be raised.
• the height H of liquid metal is generally given relative to the bottom of the injection device (6), and preferably relative to the center of the injector (23).
• the plunger (s) is (are) preferably made of a refractory material, inert with respect to the liquid metal, such as a ceramic, so as to be able to remain immersed for a long time (s) in liquid metal without risk of degradation or pollution.
• the material is preferably non-porous, so as to limit pollution of the liquid metal, in particular during alloy changes.
• the volume V of the plunger (s) (30) is approximately at least equal to the product of the area of the free surface (20) of the liquid metal (2) and the maximum variations in height to be corrected.
• a diver whose volume is at least equal to 2 x 0.6 mm x 20,000 cm 2 must be provided 2400 cm. This corresponds, for example, to a plunger of cylindrical shape with a height of about 40 mm and a diameter of about 140 mm.
• the injection device (6) is supplied with liquid metal (2), typically using a chute (7).
• the control method of the invention can be combined with a method of controlling the supply of liquid metal (2) to the injection device (6).
• the control method according to the invention then provides precise regulation and adjustment of the height of the liquid metal which completes the rough control of the height of the metal provided by the feed control method.
• the control method according to the invention can be included in a control method of the continuous casting machine (1).
• the invention also relates to a device (40) for controlling the height H of the liquid metal (2) contained in an injection device (6) of a continuous casting machine (1), capable of implementing the method of the invention.
• This device comprises at least one plunger (30) and means (41, 31, 32) for modifying the position of the (or each) plunger (30).
• the device also comprises means (11, 12) for detecting the height H of the liquid metal (2).
• the means (11, 12) for detecting the height H of the liquid metal (2) comprises a metal level sensor (11), which is typically a capacitive sensor, and a detection circuit (12), which can translate, if necessary, the sensor signal into a determined signal representative of the actual height of the liquid metal (2).
• Figure 4 illustrates such a device.
• the means (41, 31, 32) for modifying the position of the plunger (s) (30) may typically comprise a control circuit (41), an actuator (32) and a fixing and support means (31 ) of the diver (s) (30).
• the actuator makes it possible to immerse a determined part of the plunger (s) (30) in the liquid metal (2) and to move it, typically from bottom to top, and vice versa, i.e. lower it by a determined quantity ⁇ X- when H ⁇ Ho, so as to raise the level of liquid metal and raise it by a determined quantity ⁇ X + when H> Ho, so as to lower the level of liquid metal .
• the control circuit (41) which is typically connected directly to the detection circuit (12), controls the actuator (32) according to the movements of the plunger (s) (30) required to correct the height H of the liquid metal (2).
• These means can be easily automated or controlled by computer.
• the control circuit (41) makes it possible to compare the measured height H, known by the signal from the detection circuit (12), with the set height Ho.
• the height control device (40) is associated with a device for controlling the supply of liquid metal (50), as illustrated for example in FIG. 5.
• the device control (40) then ensures regulation and precise adjustment of the height of the liquid metal which completes the rough control of the height of the metal provided by the device (50).
• the device according to the invention can also be included in a device for controlling the continuous casting machine (1).
• the control device (50) comprises, for example, a feed chute (7) provided with means (9, 11-15) for controlling the flow of liquid metal poured into the injection device (6).
• the control means (9, 11-15) comprise a metal level sensor (11), which is typically a capacitive sensor, an electronic control circuit comprising a detection circuit (12) and a control circuit (13) , an adjustable opening (9) closed in a controlled manner by means (15), which is actuated by the means (14) under the control of the circuit (13).
• the level sensor (11) and the detection circuit (12) are advantageously common to the device for controlling the height of the liquid metal according to the invention and to the device for controlling the metal supply liquid.
• the invention also relates to the use of at least one plunger (30) to control the height of the liquid metal contained in a liquid metal supply device, such as an injection device.
• the subject of the invention is also a process for the continuous casting of a metal strip (3) in which an injection device (6) is supplied with liquid metal (2), characterized in that the height H of the liquid metal (2) contained in the injection device (6) using the control method of the invention.
• the supply rate of the injection device (6) in liquid metal (2) can also be regulated.
• Said metal strip typically has a width greater than or equal to approximately 1000 mm, or even greater than or equal to approximately 2000 mm.
• Said strip is typically made of aluminum or an aluminum alloy.
• the invention also relates to a continuous casting machine (1) for a metal strip (3) comprising an injection device (6) and characterized in that it comprises a height control device (40) H of the liquid metal (2) contained in the injection device (6) according to the invention.
• the continuous casting machine according to the invention is also characterized in that it is capable of allowing the casting of strips having a width greater than or equal to approximately 1000 mm, or even greater than or equal to approximately 2000 mm.
• the invention is suitable for the continuous casting of strips of aluminum or aluminum alloy, but can be applied to the continuous casting of any liquid metal.
• FIG. 6 represents a possible embodiment of the mechanical part (30, 31, 32) of the device according to the invention.
• This comprises a plunger (30), a rod (31) for supporting the plunger and an actuator (32).
• the actuator (32) comprises a metal bar (33), preferably substantially horizontal, which is fixed to a support (39), so that it can pivot freely around an axis (35), and is provided with a counterweight (36).
• the actuator (32) further comprises a cam (37) of substantially spiral shape (close to a spiral) whose radius increases regularly from a minimum value RI to a maximum value R2 over an angle ⁇ .
• the cam (37) bears against the bar (33), preferably on the side of the counterweight (36).
• the pivoting of the cam (37) around an axis (38) using, for example, a stepping motor, makes it possible to pivot the bar (33) around the axis (35 ) in a controlled manner.
• the pivoting of the bar (33) causes movements from top to bottom, or from bottom to top, of the plunger (30).
• the stroke C of these movements is linked to the difference between RI and R2, the support distance D and the distance between axes E.
• D / E 1.25

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
• Continuous Casting (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8848863

Family Applications (1)

Country Status (4)

Families Citing this family (2)

Family Cites Families (5)

• 2000
  • 2000-04-04 FR FR0004307A patent/FR2806947B1/fr not_active Expired - Fee Related
• 2001
  • 2001-04-02 WO PCT/FR2001/000975 patent/WO2001074517A1/fr not_active Application Discontinuation
  • 2001-04-02 AU AU48437/01A patent/AU4843701A/en not_active Abandoned
  • 2001-04-02 EP EP01921445A patent/EP1272298A1/de not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events